Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus for time-sequentially obtaining a plurality of medical images, an image processing method, and a storage medium for storing a program for making the image processing apparatus operate.
Description of the Related Art
As medical image imaging apparatuses (modalities) for imaging a medical image, there are an X-ray computed tomography apparatus (X-ray CT), a nuclear magnetic resonance imaging apparatus (MRI), an ultrasonic image diagnosing apparatus (US), and the like.
The medical image imaging apparatus can obtain tomographic images of an object to be examined (for example, human body) by a plurality of time phases and generate a moving image by medical images which were time-sequentially obtained. Thus, a motion of an organ is observed and a normal region and an abnormal region of the organ can be discriminated. The organs which are observed by using moving images are mainly lungs which work by a respiration, a heart which works by a heartbeat, and the like. For example, an adhesion between a lung surface and a chest can be known from a result of a motion analysis of the lungs before a surgical operation. A structural fluid analysis of a blood vessel is performed from the moving image of the heart and a stricture of the blood vessel of the heart can be known from a result of the structural fluid analysis.
In order to correctly perform those analyses, in images within a range from a predetermined time phase to another time phase among images constructing the moving image, it is necessary to accurately detect a position of an observation target. However, in the case of imaging a moving image of a movement of a human body, images (still images) constructing the moving image are not always suitable for an image process.
For example, when a motion of an organ is higher than an imaging speed of the imaging apparatus, there is a case where noises called “motion artifact” are included in the image. In such a case, since such an image that an outline of the blood vessel or organ is seen like a double image is obtained, an image quality deteriorates, it is difficult to specify corresponding positions between the images, and a detecting precision of the position of the organ (outline of the organ or blood vessel) deteriorates.
To solve such a problem, a method of detecting a position of an observation target (organ) by using images at a motion start time point and a motion end time point when a motion of the observation target is slow is used. However, when a transformation amount of the observation target is large between the images, a detecting precision of the position of the observation target deteriorates. Therefore, when an absolute value of the motion of the observation target (organ) is large, it is difficult to detect the position of the observation target from the images at the motion start time point and the motion end time point and the position detecting precision deteriorates. Therefore, in order to maintain the high position detecting precision even when a change amount of the observation target is large, a method of using the images between the motion start time point and the motion end time point is necessary.
The Official Gazette of Japanese Patent Application Laid-Open No. 2005-323994 discloses a method whereby among a plurality of images which were time-sequentially obtained, a positional deviation is corrected between the adjacent images and such a correcting process is repeated until a position matching is finished.
However, according to the method disclosed in the Official Gazette of Japanese Patent Application Laid-Open No. 2005-323994, nothing is considered about an influence of a low image quality in the correction of the positional deviation. Therefore, if the image quality of the selected image for the positional deviation correction is deteriorated, the position detecting precision deteriorates and its influence is exerted until the end of the position matching.
The invention is made in consideration of the foregoing problem and it is an aspect of the invention that among a plurality of images which were time-sequentially obtained, conformities of the images are calculated and a position of an observation target is detected by using the image having a predetermined conformity, thereby improving a position detecting precision.